For the layer-wise construction of three-dimensional objects from photo- and particularly light-hardening polymers or resins, various processes are mentioned in the literature, see “Automated Fabrication—Improving Productivity in Manufacturing” by Marshall Burns, 1993 (ISBN 0-13-119462-3).
Three variants fall under the described processes, where the layer to be generated is selectively illuminated through a transparent reference plane, a so-called “contact window” 12 (contact window), and polymerized/hardened at this plane. The three variants are sketched in FIGS. 8A-C.
In order to separate the hardened material layer from the contact window/the reference plane, a solution is described in the patent documents U.S. Pat. No. 5,171,490 (Efrem V. Fudim) and DE 41 25 534 A1 (EOS GmbH, Electro Optical Systems) for the separation by means of a thin film of flexible resin/polymer.
The EP 0 484 086 A1 describes the application, in the construction/reference plane, of a separation film which is in a semi-permeable form, in order to be permeable in one direction towards a deformable coating mixture, but to be impermeable in the opposite direction towards the photopolymerizable resin. By the permeation of the deformable coating mixture, the adhesive forces of the film towards the hardened layer shall be reduced. The deformable coating mixture may be a gas, a liquid or a gel, i.e. a fluid. The film is fixed in a frame. A frame translation device executes a translation movement after the photohardening of each layer, respectively. Due to the fixation in the frame and the additional provision of the deformable coating mixture, the stress on the semi-permeable film is high.
In EP 0 435 564 and, in another form, in EP 0 466 422 a transparent plate is required for the separation process, whereby a film, which is fixed above the plate, is subjected to tension.